Ok, then with that, SX. Actually.. either way, SX. The Q sounds better most likely, but it all depends on install too.. you can make a Q sound like shit.. and an SX sound like it's an SQ woof with SPL qualities (SQL basically), but personally the SX will handle the power better i think.
I did some measuring yesterday and if I go with the single 15 I won't save any space compared to my current setup. Looks like I'll be getting a 12. Same power but the enclosure would either be 2 cubes @32 or 3 cubes @35.....